Since the quilting design is mainly in the center, it sounds like, I would just do stitch in the ditch for the rest of it. Although it is a lot of sitd for a log cabin, you don't really have to do every seam. Just enough to stabilize it. Your center will then be the focal point. You could also do a search on this site for log cabin quilts and quilting to find some examples. I recently quilted a log cabin on my home sewing machine on which I did feathers in the lightest section and sitd on the rest.